1. Field of the Invention
The present invention relates to a distance detecting system for a moving body like an automobile. More specially, the present invention is directed to an automobile distance detecting system capable of detecting a distance to an obstacle more precisely by controlling a sensitivity of the image system and processing a picture image into an appropriate image signal.
2. Description of the Prior Art
Automobiles have been an indispensable existence to the modern society because of their expediency and comfortableness. On the other hand, the number of accidents caused by automobiles are increasing year by year and a great concern is paid for decreasing those accidents. One aspect of means for decreasing them is asked in automobiles themselves, that is to say, developing vehicles which are able to avoid accidents autonomously by judgments of the automobiles themselves. To avoid collisions autonomously, first of all, it is most important to detect an object to hamper a running of a vehicle and on the other hand it is necessary to recognize the position where the detected obstacle is placed on the road. As promising means for attaining these purposes, recently such a technique as imaging a scenery outside of a vehicle by a video camera using a solid-sate component like a CCD (Charge Coupled Device) mounted on the vehicle, and measuring a distance from the vehicle to the object by making an image process on the imaged picture, has been introduced. For example, Japanese patent application laid-open No. 197816 (1984) discloses a technology in which a three-dimensional position of an obstacle is calculated based on images taken by two video cameras mounted on a front part of the vehicle. This technique employs a so-called stereoscopical method based on a principle of triangulation and more specially the method includes a technique for measuring a distance to an obstacle by extracting the obstacle from a two-dimensional brightness distribution pattern and then obtaining a positional difference of the obstacle images on the two image pictures. However, in this method an accuracy for measuring distance is deteriorated due to the difference of brightness between the right image and the left one when there is a discrepancy of sensitivity between two cameras. To overcome the above shortcoming, as illustrated in FIG. 26, there is a prior art system using a CCD camera 101 equipped with an auto-iris lens 100 which automatically adjusts a diaphragm thereof according to an amplitude of an iris signal from the CCD camera 101 (for example, a larger amplitude when it is bright and a smaller amplitude when it is dark). From hence, it is easily considered that this auto-iris lens is applied to the abovementioned stereoscopical method. However, even with this improved apparatus there is still a problem in a distance detecting accuracy because each of the right and left auto-iris lens has an inherent characteristic which causes differences in the diaphragm setting or the diaphragm operational time between the two lenses, thereby a small discrepancy of brightness is caused between the right and left images. Also a still further problem is that the apparatus is unable to follow such a condition as illuminance changes rapidly, for instance, a case where a vehicle goes into or comes out of tunnels, because of a time lag of the auto-iris mechanism.
Further, Japanese patent application laid-open No. 188178 (1989) proposes an image display apparatus for vehicle which can catch a following vehicle securely. More specially the apparatus has ensures that a vehicle driver to recognizes the following vehicle (a vehicle running behind) even during a night running without being blinded by the headlights of following vehicles by means of correcting a brightness in a high brightness zone when comparing means detect a larger image signal than a predetermined standard value during the image processing of roads and surrounding vehicles.